Character mistake: At the end of the movie, when Jaggu is listening to the sounds recorded by PK, the audio contains the question which she asked, "Tumhare planet pe sab aise hi hote, bade kan wale?" but does not contain the answer which PK gave, even though he was sitting right there. This seems to suggest that PK did not exist in the real world.

Chosen answer:This would be a complex speculation question. But first off, it's not the vocal chords that allow humans to speak as we do, other animals have vocal chords, yet can't speak. It's about our mouths and muscle structure that allows us to "shape" sounds into words. Given the humanoid figure of PK (i.e. small, non protruding mouth and neck length), we can assume PK's species developed the ability to speak and then evolved past that, but maintained the needed structure for speaking for whatever reason, such as eating.